1. Field of the Invention
The present invention relates to a printing system capable of accepting a plurality of jobs, and a control method thereof.
2. Description of the Related Art
In a conventional printing industry, a publication is issued through various work steps such as entry of a document, designing of the document, layout editing, comprehensive layout (presentation by printing), proofreading (layout correction and color correction), proof (proof print), block copy preparation, printing, post-processing, and shipping.
In the conventional printing industry, an offset reproduction printing press has been used in the printing step, requiring the block copy preparation step. However, once the block copy is prepared, it is difficult to correct the block copy. If the block copy is corrected, the cost rises. In block copy preparation, therefore, careful proofreading (i.e., careful layout check and color confirmation) is indispensable. Some period of time is generally taken until a publication is issued.
Most apparatuses used in respective work steps are bulky and require expert knowledge, and know-how of experts is indispensable.
In this situation, POD (Print On Demand) printing systems using electrophotographic and inkjet printing apparatuses are proposed recently.
(See Japanese Patent Laid-Open Nos. 2004-310746 and 2004-310747).
The POD printing system does not require the above-mentioned block copy preparation and other complicated work steps.
As for sheets (print media) used in the POD market, the printing system may process various types of sheets in order to receive a variety of printing orders from customers. In this situation, an operation to separate and convey a print medium from a feeding apparatus serving as an example of a print medium supply source may change from that for a general sheet. For example, the printing system can process a print medium of a type different in surface property, glossiness, and thickness from a print medium such as plain paper. For this reason, print media which should be separated and fed one by one from a feeding apparatus may be conveyed simultaneously. A state in which print media are conveyed while at least partially overlapping each other is defined as “multi feed (double feed)”. If multi feed occurs, problems such as a fixing error, a jam in the printing apparatus, and mixing of a blank sheet arise. It is desirable to detect multi feed before conveying multi-fed sheets into the printing unit of the printing apparatus, and discharge the multi-fed sheets outside the apparatus.